System Software Abstraction Layer - much more than Operating System Abstraction Layer

摘要

Current and future aircraft systems require real-time embedded software with greater flexibility compared to what was previously available due to the continuous advancements in the technology leading to large and complex systems. Portability of software as one of the aspects of this flexibility is a major concern in application development for avionics domain for fast development and integration of systems. Abstractions of the hardware platform which have been already introduced by the operating system community allow the software modules to be reused on different hardware and with different physical resources. Now operating system community has come up with an abstraction layer called operating system abstraction layer (OSAL) which along with the hardware abstraction unifies the OS architecture too. It provides a common set of primitives independent of the underlying operating system and its particular architecture. Factors such as reliability, scalability and determinism of any application largely depend on the design and architecture of the application. This is the most important and critical factor of real time systems such as mission computers of avionics systems, missile control system or control computers of space shuttle. It demands developer to perform feasibility of different software architecture to select the best alternative. Authors' analysis shows that to make any real time application more secure, scalable, deterministic, and highly portable, OSAL has to be extended to more than just operating system abstraction. This new view of OSAL will be called as system software abstraction layer (SSAL). In this paper, authors attempt to highlight the efficiency of SSAL as well as detailed description of its main features and design considerations. Authors have implemented the SSAL on top of two well known OS (WinCE and Vxworks) and performed extensive evaluations, which shows that it effectively reduces portability efforts while achieving simplicity, predictability, security and determinism. This paper presents in brief, the API functionalities, its components, implementation, interfaces, advantages and overheads along with a case study.